This disclosure is related to application SN 078,127 filed July 27, 1987 now U.S. Pat. No. 4,853,014 and assigned to the Assignee of the present disclosure. As set forth in that disclosure, installation of process plant equipment involves the process of directing steam through the piping of a plant for initial cleaning purposes. For a typical situation, that disclosure describes how the plant boiler is operated to make steam which is directed through various conduits and pipes of the plant and further describes how a temporary conduit is installed to route the steam so that the plant piping is cleaned. The disclosure goes on to set forth difficulties in venting the flow of steam. Many difficulties arise in the handling of the steam, particularly at the venting step after the cleaning process has been completed. There are three primary difficulties related to the steam venting, one being the noise of venting, another being the derivative sonic backpressure wave which is formed during venting, and the third is the reactive force acting on the vent line. The static backpressure wave established restricts venting so that the volume of steam passing through the vent is reduced. When this occurs, it completely changes the rate of flow in the plant piping and may regrettably reduce the cleaning action which occurs.
The foregoing disclosure is directed to various features for handling these problems including the introduction of a water spray for the purpose of cooling and decelerating the steam flow. Moreover, the prior disclosure sets forth a mode and mechanism for injecting water spray as a mist in intimate contact with and mixed intimately with the steam to thereby avoid the backpressure resulting from the sonic shock wave. In the present disclosure, it has been discovered that there are optimum rates of introduction of water and air. The water is sprayed into the steam flow which is traveling almost at sonic velocity. The present process is especially effective where the steam velocity is at least about 35% of sonic velocity to just below sonic velocity. It is ideally operated just below sonic velocity, in other words, typically in the range of 75-90% of sonic velocity. The present process involves adjusting the rate of water flow so that an optimum is achieved. Water is the ideal cooling and decelerating material. The rate of flow is increased from zero. Obviously, an axiom that more is better might well prevail. However, there is an optimum water rate. Increasing the water flow above the optimum has detrimental effects on the system. The optimum rate of water introduction occurs at when rate of water misted into the flow causes the velocity to decelerate from some maximum velocity down to about 35% of sonic velocity. If the velocity drops below that, there is the consequential probability of water droplets separating from the steam in the piping system downstream of the mist injection. Accordingly, one feature of the present disclosure is the process of optimizing the water flow so that deceleration is accomplished down to about 35% of sonic velocity but does not go much therebelow and run the risk of separating in the piping system. With excessive water addition and/or flow velocities below the optimum, the water mist will separate from the steam forming an annular film on the pipe wall. This film of water will travel at velocities less than the steam conveyed in the center of the pipe and the benefit of momentum transfer by further water addition is lost. In addition, the water film on the pipe wall has the effect of reducing the cross-sectional area available for steam flow which has the effect of increasing the system backpressure.
An important feature of the present disclosure is the added step of introducing large volumes of air along with the water mist. The air is introduced, not in fixed quantity, but at a rate that is determined by the pressure differential arising from eduction. Ideally, air is introduced at or about the region where water mist is introduced so that the two added fluids markedly cool and decelerate the steam flow, thereby resulting in the desired dissipation of the steam at venting, avoiding the formation of noise, and avoiding the formation of a backpressure sonic wave. Addition of large volumes of air into the steam at the same point of water addition results in the greater atomization of the water jet due to the fact that the water surface violently erupts as a result of the vaporization of the water. The addition of copious amounts of air reduces the vapor pressure of the water, increasing the resultant vaporization of the water and thus increases the breakup of the injected jet, the formation of a fine dispersed mist and enhances the momentum transfer from the steam to the injected fluids. This vaporization also converts thermal energy from the steam to vaporization energy, thus cooling the aggregate flow to reduce specific flow volume and therefore fluid velocity. Addition of copious amounts of air also enhances system safety since, in the event water supply is lost, the mass of air educted will be sufficient to cool and decelerate steam to avoid sonic waves and also keep reactive forces within safe limits. The air educting apparatus preferably includes an external air inlet directed into the pipe where the steam flow is located, is directed downstream so that eduction occurs, thereby introducing a variable quantity of air. Moreover, air is educted in one embodiment through a flow controlled butterfly valve which opens in proportion to the air flow to provide automatic air flow regulation. Air induction can be enhanced by use of the water mist as a momentum source. Compressed air expanding through a nozzle can also be used to enhance air induction. Blowers or fans may also be used to increase the air flow to the eductor.
The foregoing is developed in several embodiments as illustrated, various embodiments using single sets of such equipment, and alternate embodiments showing first and second sets of such equipment. One advantage of the present procedure is the incorporation of a temporary pipe which has increasing diameter so that steam flow through the piping is permitted to expand during deceleration. Such expansion involves temporary piping which incorporates a frustoconical pipe section making a transition from a smaller to a larger diameter. More than one such frustoconical section can be used as required to limit backpressure to acceptable levels while minimizing the cost of the installed temporary pipe.
While the foregoing is directed to certain features of the preferred embodiment of the present disclosure, details relating to the present procedure will be more readily understood upon a review of the below written specification in conjunction with the drawings which are appended to the present disclosure.